Fly ash is the by-product of the combustion of coal. Disposal of fly ash is expensive. Thus, there are ongoing efforts to identify uses for fly ash. Fly ash is presently used as a concrete admixture, as a soil stabilizer, and as a filler for asphalt and structural materials, such as bricks.
The concrete industry serves as one of the most important commercial outlets for fly ash, since fly ash is used in concrete as a partial replacement for Portland cement. However, high levels of unburned carbon can make fly ash samples unusable as a concrete filler. Carbon in the fly ash interferes with the action of air entraining admixtures, or specialty surfactants, which are used to stabilize air bubbles in concrete mixtures. Measurements made on a variety of model additives suggest that admixtures are adsorbed by carbon surfaces from the aqueous phase. The adsorption process is believed to occur preferentially on nonpolar carbonaceous surface area.
Exposing fly ash to air at high temperatures, called thermal air oxidation, reveals a change in surface chemistry that occurs just prior to combustion of carbon in fly ash. The surface oxidation has the effect of changing a carbon property so that fly ash can be effectively utilized in cement-containing mixtures. Unfortunately, thermal air oxidation is an impractical industrial process because temperatures on the order of 400.degree. C. are required to effectively passivate carbon.
Additionally, processes utilizing other oxidizing agents such as hydrogen peroxide (H.sub.2 O.sub.2) and nitric acid (HNO.sub.3) are available. The problem with these other processes is that the oxidizing agents are liquid. Wet treatments make fly ash difficult to handle, transport, and use.
In view of the foregoing, it would be highly desirable to provide an inexpensive and practical technique that allows deactivation of carbon within fly ash samples. The technique should reduce the surfactant adsorptivity of carbon without detrimentally changing other properties of the fly ash. Furthermore, the technique should be a dry process that functions at low temperature.